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  • Modeling Pharmacokinetics and Pharmacodynamics on a Mobile Device to Help Caffeine Users

    Frank E. Ritter and Kuo-Chuan (Martin) Yeh

    The Pennsylvania State University {frank.ritter, martin.yeh}@psu.edu

    Abstract. We introduce a mobile device application that displays key information about caffeine: the pharmacokinetics (time course of drug levels) and pharmacodynamics (the effects of caffeine level) visually on the iPhone, iPod Touch, and iPad. This application, Caffeine Zone, is based on an existing model of caffeine physiology using user inputs, including caffeine dose, start time, and consumption speed. It calculates the caffeine load in a user for the next twenty-four hours and displays it using a line chart. In addition, it shows whether the user is currently in the cognitive alert zone (the range of caffeine where a normal person might benefit most from caffeine) or the possible sleep zone (the range of caffeine where sleep is presumed not affected by caffeine level.) Understanding the pharmacokinetics and pharmacodynamics of caffeine can help people using caffeine to improve alertness, including in operational environments. Caffeine Zone may also help users create a mental model of caffeine levels when the device is not available. We argue that this app will both teach users the complex absorption/elimination process of caffeine and help monitor users daily caffeine usage. The model, with additional validation, can be part of a system that predict cognitive state of users and provide assistances in critical conditions.

    Keywords: pharmacokinetics, pharmacodynamics, caffeine, mobile app, modeling

    1 Introduction

    Caffeine, the most widely used psychoactive substance [e.g., 1, 2], has long been regarded as an effective way to improve mental alertness and reactions, especially in critical operational environments like long-distance driving [e.g., 3], air traffic control, and nearly all operational military environments. Caffeine can be found in many different sources of foods, beverages, and medicines, including chewable gum in military rations. Some people take caffeine-contained substances, mainly coffee and tea, for well-being [2]; others for its pharmacological effects. Low to moderate doses of caffeine can indeed be very useful in military settings according to the National Academys Institute of Medicine [4].

    Overuse of caffeine, however, can impair cognition and health directly and indirectly. For example, higher levels of caffeine can lead to higher levels of cortisol [5]. Too

    Ritter, F. E., & Yeh, K.-C. M. (2011). Modeling pharmacokinetics and pharmacodynamics on a mobile device to help caffeine users. In Augmented Cognition International Conference 2011, FAC 2011, HCII 2011, LNAI 6780, 528-535. Springer-Verlag: Berlin Heidelberg.

  • much caffeine may disrupt sleep schedules1 and may contribute to long-term chronic health issues such as agitation, anxiety [6], and insomnia. Users in stressful, high tempo situations might be particularly prone to using and overusing stimulants to maintain alertness (e.g., see a Naval Aerospace Medical Research Laboratory report [7]). Striking a balance between too much and too little is a challenging task because caffeines use depends on understanding the pharmacokinetics of caffeine, because uptake and excretion are exponential processes, and because while the immediate benefit is during the task, the delayed response to eliminate caffeine may make users more sleep deprived later and over time. The computation and future impact of use may be beyond many of us to compute.

    As a result, people who use caffeine for its pharmacological effects can end up with at least three possible problems. They can consume too little, and not be as alert as they need to be. They can consume too much at a single point in time and be jittery or have other side effects. Or they can consume a right amount but too close to when they would like to sleep and subsequently have trouble sleeping.

    Before introducing an application to help users moderate their caffeine levels, we will briefly describe the caffeine model.

    2 Understanding Non-linear Curves

    We model two of the processes in the human body that modify the caffeine level: absorption and elimination. Absorption refers to caffeine being taken into bloodstream from its external form (liquid, tablet, gum, etc.). Elimination refers to caffeine being excreted from our body, mostly through urine. Both absorption and elimination rates are non-linear functions based on time. (We subsume distribution with absorption and metabolism with elimination.)

    In our theory and in the software, we use the following equations taken from a review used for modeling caffeine in cognitive models and agents [8]:

    Caffeine absorption t+1 = Caffeine intake reservoir t * e(1/7min) (1)

    Caffeine elimination t+1 = Caffeine in bloodstream t * e(1/240min) (2)

    That is, we have an absorption half-life of 7 minutes (eqn. 1) and an elimination half-life of 4 hours in (eqn. 2).

    1 The effect of caffeine on sleep varies. Some people are very sensitive to caffeine; some seem

    to have no sleep problems despite regular caffeine consumption in the evening [2].

    Ritter, F. E., & Yeh, K.-C. M. (in press, 2011). Modeling pharmacokinetics and pharmacodynamics on a mobile device to help caffeine users. In Augmented Cognition International Conference 2011, FAC 2011, HCII 2011, LNAI 6780, 528-535. Springer-Verlag: Berlin Heidelberg.

  • Soon after caffeine intake, the absorption and elimination processes start simultaneously: caffeine is being distributed into the bloodstream and excreted into urine. The exponential decay equations intertwined with one another may make it difficult for caffeine users to calculate the current caffeine intake in their bloodstream at any moment without external computation, and particularly difficult to predict the level in several hours when it will be time to sleep. This complexity is the major source of the aforementioned challengestriking a balance of caffeine dose over time.

    3 Caffeine Zone

    Caffeine Zone is an application that utilizes the ubiquity and computational power of modern mobile devices such that an inexpensive and portable real-time caffeine intake can be displayed graphically. The current version of Caffeine Zone works on the iOS operating systemprovided on iPhone, iPod Touch, and iPadversion 3.1.2 and above. There is, however, no conceivable reason it cannot be ported to other mobile devices such as the Android, BlackBerry, and similar devices.

    3.1 Software Architecture

    The software architecture of Caffeine Zone is shown in Figure 1, providing also an overview of the functions in the app. The application consists of three major components: main, history, and settings. The main component is where the formula are calculated and displayed; the history component is in charge of recording/managing the consumption history; the settings component is the center where settings are achieved and retrieved. The data points of caffeine intake are calculated for each minute and stored in the SQLite database that comes with iOS to save calculation time whenever the line plot is to be displayed.

    Ritter, F. E., & Yeh, K.-C. M. (in press, 2011). Modeling pharmacokinetics and pharmacodynamics on a mobile device to help caffeine users. In Augmented Cognition International Conference 2011, FAC 2011, HCII 2011, LNAI 6780, 528-535. Springer-Verlag: Berlin Heidelberg.

  • Fig. 1. The software architecture of Caffeine Zone

    3.2 The Pharmacokinetics Equations and Assumptions

    We provide several parameters as defaults. These numbers are extracted from previous research in the pharmacology effects of caffeine. They are the half-life of absorption and excretion (currently implemented in the calculation and are unchangeable), and the thresholds for minimum optimal caffeine for cognition and maximum optimal caffeine for cognition. We also include a threshold for sleep. Weight is used to calculate dosage (dose by weight) and units to display, doses (mg), or dosages (mg/kg).

    The minimum and maximums for the cognitive range are based on our review [8], and assume that the users are typical, which not all users are. These two numbers represent the minimal does of caffeine that can keep humans alert or that helps cognitive performance and the maximum dose of caffeine that does not impair cognition.

    The half-lives are taken from our review. We know that the half-life of elimination should be moderated for nicotine users [9]. In general, the half-life for nicotine users is about half as long as for non-nicotine users. We intend to add this effect in a future revision. The threshold for sleep is currently taken from anecdotal reports by the developers.

    These parameters will vary from person to person. Therefore, these parameters are adjustableusers can change the settings based on their usage.

    Ritter, F. E., & Yeh, K.-C. M. (in press, 2011). Modeling pharmacokinetics and pharmacodynamics on a mobile device to help caffeine users. In Augmented Cognition International Conference 2011, FAC 2011, HCII 2011, LNAI 6780, 528-535. Springer-Verlag: Berlin Heidelberg.

  • Fig. 2. The interface for Caffeine Zone, showing on the left some of the adjustable parameters, and on the right, the scrollable pharmacokinetics display.

    3.3 The Displays

    Figure 2 shows two of the current displays, including the timeline of caffeine. By displaying the caffeine model users can understand the time course of their caffeine levels, and moderate their caffeine consumption more effectively. For example, they can switch to decaf co

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